Environmental flow assessment for intermittent rivers supporting the most poleward mangroves

Potential distribution projections of mangrove forests and invasive plants under climate change: case insights from mangrove management in Guangdong Province, China

Mangrove ecosystems are vital for maintaining biodiversity, purifying water, sequestering carbon, and mitigating climate change in coastal regions. The geographical distribution of mangrove forests has been severely affected by global warming; therefore, it must be predicted under future climate scenarios to provide a scientific basis for conservation and restoration. In this study, we employed the MaxEnt model to predict the potential distribution of suitable mangrove areas in Guangdong Province under current conditions and two future climate scenarios (2030s and 2090s): SSP1-2.6 and SSP5-8.5. The potential distributions of introduced mangrove plants (Laguncularia racemosa and Sonneratia apetala) were assessed to evaluate their suitability for mangrove restoration. Furthermore, we investigated the invasive potential of Spartina alterniflora, a biologically invasive species in mangrove ecosystems, under different climate scenarios. Finally, a conservation gap analysis was conducted to identify priority areas for mangrove protection. We observed the following: i) main environmental factors affecting the distribution pattern of mangroves in Guangdong Province were temperature and water quality; ii) hotspots of mangrove distribution are mainly concentrated in the Beibu Gulf coastline, Leizhou Gulf coastline, Zhenhai Bay-Dongping Harbor-Beijin Bay coastline, Zhuhai Harbor-Guangzhou Bay-Humen-Mawan Bay, Shuangyue Bay, and Rongjiang River estuary; iii) optimal zone of mangroves was the largest under the SSP5-8.5 scenario, and the potential suitable zone and geometric center of mangroves gradually shifted to higher latitudes; iv) the protection and restoration of mangroves should be prioritized in the future in the zones of Anpu Harbor, Leizhou Bay, Zhenhai Bay, and Huangmaohai and coastline of Pearl River Estuary.

Enhancing nutrient absorption through the influence of mangrove ecosystem on flow rate and retention time in salt marshes

This study investigates the impact of pneumatophores (the aerial roots of Avicenna marina) on water flow rate, retention time, contact time, and consequently on nutrient absorption through the sediment in sub-tropical salt marshes. The goal is to realize how the density of mangroves in salt marshes influences the kinematic factors of streamflow at estuaries. To this end, a field experiment was carried out to assess nutrient and organic compound levels in the sediment and water samples, spanning six sampling stations along the Chabahar River discharging to the Chabahar Bay, Iran. Then, we delved into the influence of altering environmental parameters, such as density and geometry, on the kinematic features of the flow through statistical analysis and hydraulic modeling. The results showed that the aerial roots reduce the flow rate and increase both retention and contact times. The longest retention time was observed at station #5 due to increased vegetation density and decreased instream velocity. In addition, measurements of total organic matter, total organic carbon, and total nitrogen indicated that an extended contact time resulted in increased absorption flux to the stream by sediments. As a result, pneumatophores can serve as an effective sink for organic matter in ecotones in salt marshes.